CVE-2021-41228: Code injection in `saved_model_cli`

TensorFlow’s saved_model_cli tool is vulnerable to a code injection as it calls eval on user supplied strings

def preprocess_input_exprs_arg_string(input_exprs_str):
...
for input_raw in filter(bool, input_exprs_str.split(';')):
...
input_key, expr = input_raw.split('=', 1)
input_dict[input_key] = eval(expr)
...

This can be used by attackers to run arbitrary code on the plaform where the CLI tool runs. However, given that the tool is always run manually, the impact of this is not severe. We have patched this by adding a safe flag which defaults to True and an explicit warning for users.